1. Field of the Invention
The present invention relates to a microphone array system. In particular, the present invention relates to a system including two microphones arranged on one coordinate axis that estimates a sound to be received in an arbitrary position on that dimensional axis by performing received sound signal processing and thus can estimate sounds in numerous positions with a small number of microphones.
2. Description of the Related Art
Hereinafter, a sound-estimation processing technique utilizing a conventional microphone array system will be described.
A microphone array system includes a plurality of microphones, and performs signal processing by utilizing sound signals received at each microphone. The objectives, the structures, the use and the effects of the microphone array system are varied significantly by how microphones are arranged in the sound field, what kind of sounds are received, and what kind of signal processing is performed. In the case where there are a plurality of sound sources of desired sounds and noise in the sound field, enhancing the desired sounds and suppressing noise with high quality are main tasks to be achieved by received sound processing with microphones. Detection of the positions of the sound sources is useful for various applications such as teleconference systems, guest-reception systems or the like. In order to realize processing for enhancing a desired sound, suppressing noise and detecting the position of a sound source, it is useful to use the microphone array system.
In the conventional technique, in order to improve quality in enhancing a desired sound, suppressing noise and detecting the position of the sound source, signal processing is performed with an increased number of microphones constituting the array in order to obtain more data of received sound signals. FIG. 17 shows a microphone array system used for desired sound enhancement processing by conventional synchronous addition. In the microphone array system shown in FIG. 17, reference numeral 171 denotes real microphones MIC0 to MICnxe2x88x921 constituting a microphone array, reference numeral 172 denotes delay units D0 to Dnxe2x88x921 for adjusting timing of the signals of the sounds received by the microphones 171, and reference numeral 173 denotes an adder for adding the signals of the sounds received by the microphones 171. In the desired sound enhancement by the conventional technique, a sound from a specific direction is enhanced by adding the numerous components wherein the received sound signals which become components for the addition processing are delayed for synchronization. In other words, sound signals used for the synchronous addition signal processing are increased in number by increasing the number of the real microphones 171. Thus, the intensity of the desired sound is increased. In this manner, the desired sound is enhanced so that a distinct sound is picked out. In noise suppression processing, noise is suppressed by performing synchronous subtraction. In processing for detecting the position of a sound source, synchronous addition or calculation of cross-correlation coefficients is performed with respect to an assumed direction. Thus, in these cases as well, sound signal processing is improved by increasing the number of microphones.
However, this technique for microphone array signal processing that can be improved by increasing the number of microphones is disadvantageous in that a large number of microphones are required to be prepared to realize high quality sound signal processing, and therefore the microphone array system results in a large scale. Moreover, in some cases, it may be difficult to physically arrange a necessary number of microphones for sound signal estimation with required quality in a necessary position.
In order to solve the above problems, it is desired to estimate a sound signal that would be received in an assumed position based on actual sound signals received by actually arranged microphones, instead of receiving a sound by a microphone that is arranged actually. Furthermore, using the estimated signals, enhancement of a desired sound, noise suppression and detection of a sound source position can be performed.
The microphone array system is useful in that it can estimate a sound signal to be received in an arbitrary position on an array arrangement, using a small number of microphones. The microphone array system estimates a sound signal to be received in an assumed position on the extension line (one-dimension) of a straight line on which a small number of microphones are arranged. Although actual sounds propagate in a three-dimensional space, if a sound signal to be received in an arbitrary position on one axis direction can be estimated, a sound signal to be received in an arbitrary position in a space can be obtained by estimating and synthesizing sound signals to be received in the coordinate positions on the three axes in the space, based on the estimated sound signal to be received in the position on each axis. The microphone array system is required to estimate a signal from a sound source with reduced estimation errors and high quality.
Furthermore, it is desired to develop an improved signal processing technique for signal processing procedures used for the sound signal estimation so as to improve the quality of the enhancement of a desired sound, the noise suppression, the sound source position detection.
It is an object of the present invention to provide a first microphone array system that can estimate a signal to be received in an arbitrary position on an axis by arranging two microphones on the axis.
It is another object of the present invention to provide a second microphone array system that can estimate a signal to be received in an arbitrary position on a plane by arranging three microphones on the plane.
It is another object of the present invention to provide a third microphone array system that can estimate a signal to be received in an arbitrary position in a space by arranging four microphones in the space in such a manner that they are not on the same plane.
In order to achieve the above objects, the first microphone array system of the present invention includes two microphones and a sound signal estimation processing part, and estimates a sound signal to be received in an arbitrary position on a straight line on which the two microphones are arranged. The sound signal estimation processing part expresses a sound signal estimated to be received in a position on the straight line on which the two microphones are arranged by a wave equation Equation 5, assuming that the sound wave coming from a sound source to the two microphones is a plane wave. The sound signal estimation processing part estimates a coefficient b cos xcex8 of the wave equation Equation 5 that depends on the direction from which the sound wave comes, assuming that the average power of the sound wave that reaches each of the two microphones is equal to that of the other microphone. The sound signal estimation processing part estimates a sound signal to be received in an arbitrary position on the same axis on which the microphones are arranged, based on the sound signals received by the two microphones.                                                         P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                                          i                      +                      1                                                        ,                                      y                    0                                    ,                                      t                    j                                                  )                                      -                          P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                    i                                    ,                                      y                    0                                    ,                                      t                    j                                                  )                                              =                      a            ⁢                          {                                                                    v                    x                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        i                                            ,                                              y                        0                                            ,                                              t                                                  j                          +                          1                                                                                      )                                                  -                                                      v                    x                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        i                                            ,                                              y                        0                                            ,                                              t                        j                                                              )                                                              }                                      ⁢                  
                ⁢                              {                                                            v                  x                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                                              i                        +                        1                                                              ,                                          y                      0                                        ,                                          t                      j                                                        )                                            -                                                v                  x                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                      i                                        ,                                          y                      0                                        ,                                          t                      j                                                        )                                                      }                    =                      b            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢            θ            ⁢                          {                                                p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                                                  i                          +                          1                                                                    ,                                              y                        0                                            ,                                              t                        j                                                              )                                                  -                                  p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                                                  i                          +                          1                                                                    ,                                              y                        0                                            ,                                              t                                                  j                          -                          1                                                                                      )                                                              }                                                          Equation        ⁢                  xe2x80x83                ⁢        5            
where x and y are respective spatial axes, t is a time, v is an air particle velocity, p is a sound pressure, a and b are coefficients, and xcex8 is the direction of a sound source.
By the above embodiment, a sound signal to be received in an arbitrary position on the same axis can be estimated with Equation 5 by estimating a term of b cos xcex8, regarding the average powers of the sound wave received by the two microphones as equal under the condition in which the sound wave coming from the sound source in an arbitrary direction xcex8 to the two microphones can be regarded as a plane wave. Estimation is possible with a small number of microphones of 2, and thus it is possible to reduce the system scale.
In order to achieve the above objects, the second microphone array system of the present invention includes three microphones that are not on a same straight line and a sound signal estimation processing part, and estimates a sound signal to be received in an arbitrary position on the same plane on which the three microphones are arranged. The sound signal estimation processing part expresses a sound signal estimated to be received in a position on the same plane on which the three microphones are arranged by a wave equation Equation 6, assuming that the sound wave coming from a sound source to the three microphones is a plane wave. The sound signal estimation processing part estimates coefficients b cos xcex8x and b cos xcex8y of the wave equation Equation 6 that depend on the direction from which the sound wave comes, assuming that the average power of the sound wave that reaches each of the three microphones is equal to those of the other microphones. The sound signal estimation processing part estimates a sound signal to be received in an arbitrary position on the same plane on which the microphones are arranged, based on the sound signals received by the three microphones.                                                         P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                                          i                      +                      1                                                        ,                                      y                    0                                    ,                                      t                    j                                                  )                                      -                          P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                    i                                    ,                                      y                    0                                    ,                                      t                    j                                                  )                                              =                      a            ⁢                          {                                                                    v                    x                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        i                                            ,                                              y                        0                                            ,                                              t                                                  j                          +                          1                                                                                      )                                                  -                                                      v                    x                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        i                                            ,                                              y                        0                                            ,                                              t                        j                                                              )                                                              }                                      ⁢                  
                ⁢                              {                                                            v                  x                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                                              i                        +                        1                                                              ,                                          y                      0                                        ,                                          t                      j                                                        )                                            -                                                v                  x                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                      i                                        ,                                          y                      0                                        ,                                          t                      j                                                        )                                                      }                    =                      b            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢                          θ              x                        ⁢                          {                                                p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                                                  i                          +                          1                                                                    ,                                              y                        0                                            ,                                              t                        j                                                              )                                                  -                                  p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                                                  i                          +                          1                                                                    ,                                              y                        0                                            ,                                              t                                                  j                          -                          1                                                                                      )                                                              }                                      ⁢                  
                ⁢                                            P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                    0                                    ,                                      y                                          S                      +                      1                                                        ,                                      t                    j                                                  )                                      -                          P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                    0                                    ,                                      y                    S                                    ,                                      t                    j                                                  )                                              =                      a            ⁢                          {                                                                    v                    y                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                        S                                            ,                                              t                                                  j                          +                          1                                                                                      )                                                  -                                                      v                    y                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                        S                                            ,                                              t                        j                                                              )                                                              }                                      ⁢                  
                ⁢                              {                                                            v                  y                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                      0                                        ,                                          y                                              S                        +                        1                                                              ,                                          t                      j                                                        )                                            -                                                v                  y                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                      0                                        ,                                          y                      S                                        ,                                          t                      j                                                        )                                                      }                    =                      b            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢                          θ              y                        ⁢                          {                                                p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                                                  S                          +                          1                                                                    ,                                              t                        j                                                              )                                                  -                                  p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                                                  S                          +                          1                                                                    ,                                              t                                                  j                          -                          1                                                                                      )                                                              }                                                          Equation        ⁢                  xe2x80x83                ⁢        6            
By the above embodiment, a sound signal to be received in an arbitrary position on the same plane can be estimated with Equation 6 by estimating terms of b cos xcex8x and b cos xcex8y, regarding the average powers of the sound wave received by the three microphones as equal under the condition in which the sound wave coming from the sound sources in arbitrary directions xcex8x and xcex8y to the three microphones can be regarded as a plane wave. Estimation is possible with a small number of microphones of 3, and thus it is possible to reduce the system scale.
In order to achieve the above objects, the third microphone array system of the present invention includes four microphones that are not on the same plane and a sound signal estimation processing part, and estimates a sound signal to be received in an arbitrary position in a space. The sound signal estimation processing part expresses a sound signal estimated to be received in an arbitrary position in the space by a wave equation Equation 7, assuming that the sound wave coming from a sound source to the four microphones is a plane wave. The sound signal estimation processing part estimates coefficients b cos xcex8x, b cos xcex8y and b cos xcex8z of the wave equation Equation 7 that depend on the direction from which the sound wave comes, assuming that the average power of the sound wave that reaches each of the four microphones is equal to those of the other microphones. The sound signal estimation processing part estimates a sound signal to be received in an arbitrary position in the space in which the microphones are arranged, based on the sound signals received by the four microphones.                                                         P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                                          i                      +                      1                                                        ,                                      y                    0                                    ,                                      z                    0                                    ,                                      t                    j                                                  )                                      -                          P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                    i                                    ,                                      y                    0                                    ,                                      z                    0                                    ,                                      t                    j                                                  )                                              =                      a            ⁢                          {                                                                    v                    x                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        i                                            ,                                              y                        0                                            ,                                              z                        0                                            ,                                              t                                                  j                          +                          1                                                                                      )                                                  -                                                      v                    x                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        i                                            ,                                              y                        0                                            ,                                              z                        0                                            ,                                              t                        j                                                              )                                                              }                                      ⁢                  
                ⁢                              {                                                            v                  x                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                                              i                        +                        1                                                              ,                                          y                      0                                        ,                                          z                      0                                        ,                                          t                      j                                                        )                                            -                                                v                  x                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                      i                                        ,                                          y                      0                                        ,                                          z                      0                                        ,                                          t                      j                                                        )                                                      }                    =                      b            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢                          θ              x                        ⁢                          {                                                p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                                                  i                          +                          1                                                                    ,                                              y                        0                                            ,                                              z                        0                                            ,                                              t                        j                                                              )                                                  -                                  p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                                                  i                          +                          1                                                                    ,                                              y                        0                                            ,                                              z                        0                                            ,                                              t                                                  j                          -                          1                                                                                      )                                                              }                                      ⁢                  
                ⁢                                            P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                    0                                    ,                                      y                                          S                      +                      1                                                        ,                                      z                    0                                    ,                                      t                    j                                                  )                                      -                          P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                    0                                    ,                                      y                    S                                    ,                                      z                    0                                    ,                                      t                    j                                                  )                                              =                      a            ⁢                          {                                                                    v                    y                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                        S                                            ,                                              z                        0                                            ,                                              t                                                  j                          +                          1                                                                                      )                                                  -                                                      v                    y                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                        S                                            ,                                              z                        0                                            ,                                              t                        j                                                              )                                                              }                                      ⁢                  
                ⁢                              {                                                            v                  y                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                      0                                        ,                                          y                                              S                        +                        1                                                              ,                                          z                      0                                        ,                                          t                      j                                                        )                                            -                                                v                  y                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                      0                                        ,                                          y                      S                                        ,                                          z                      0                                        ,                                          t                      j                                                        )                                                      }                    =                      b            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢                          θ              y                        ⁢                          {                                                p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                                                  S                          +                          1                                                                    ,                                              z                        0                                            ,                                              t                        j                                                              )                                                  -                                  p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                                                  S                          +                          1                                                                    ,                                              z                        0                                            ,                                              t                                                  j                          -                          1                                                                                      )                                                              }                                      ⁢                  
                ⁢                                            P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                    0                                    ,                                      y                    0                                    ,                                      z                                          R                      +                      1                                                        ,                                      t                    j                                                  )                                      -                          P              ⁢                              xe2x80x83                            ⁢                              (                                                      x                    0                                    ,                                      y                    0                                    ,                                      z                    R                                    ,                                      t                    j                                                  )                                              =                      a            ⁢                          {                                                                    v                    Z                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                        0                                            ,                                              z                        R                                            ,                                              t                                                  j                          +                          1                                                                                      )                                                  -                                                      v                    z                                    ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                        0                                            ,                                              z                        R                                            ,                                              t                        j                                                              )                                                              }                                      ⁢                  
                ⁢                              {                                                            v                  Z                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                      0                                        ,                                          y                      0                                        ,                                          z                                              R                        +                        1                                                              ,                                          t                      j                                                        )                                            -                                                v                  Z                                ⁢                                  xe2x80x83                                ⁢                                  (                                                            x                      0                                        ,                                          y                      0                                        ,                                          z                      R                                        ,                                          t                      j                                                        )                                                      }                    =                      b            ⁢                          xe2x80x83                        ⁢            cos            ⁢                          xe2x80x83                        ⁢                          θ              Z                        ⁢                          {                                                p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                        0                                            ,                                              z                                                  R                          +                          1                                                                    ,                                              t                        j                                                              )                                                  -                                  p                  ⁢                                      xe2x80x83                                    ⁢                                      (                                                                  x                        0                                            ,                                              y                        0                                            ,                                              z                                                  R                          +                          1                                                                    ,                                              t                                                  j                          -                          1                                                                                      )                                                              }                                                          Equation        ⁢                  xe2x80x83                ⁢        7            
where x, y and z are respective spatial axes.
By the above embodiment, a sound signal to be received in an arbitrary position in a space can be estimated with Equation 7 by estimating terms of b cos xcex8x, b cos xcex8y and b cos xcex8z, regarding the average powers of the sound wave received by the four microphones as equal under the condition in which the sound wave coming from the sound source in arbitrary directions xcex8x, xcex8y and xcex8z to the four microphones can be regarded as a plane wave. Estimation is possible with a small number of microphones of 4, and thus it is possible to reduce the system scale.
In the first, second and third microphone array systems, sound signal estimation processing is performed with respect to a plurality of positions, and the following processing also can be performed: processing for enhancing a desired sound by synchronous addition of these estimated signals; processing for suppressing noise by synchronous subtraction of these estimated signals; and processing for detecting the position of a sound source by cross-correlation coefficient calculation processing and coefficient comparison processing.
The microphone array system of the present invention can estimate sound signals to be received in an arbitrary position on the same axis, regarding the average powers of the sound wave received by the two microphones as equal under the condition in which the sound wave coming from the sound source in an arbitrary direction xcex8 to two microphones can be regarded as a plane wave. The present invention can estimate with a small number of, i.e., two microphones, which reduces the system scale. Moreover, by applying the same signal processing technique, the present invention can estimate sound signals to be received in an arbitrary position on the same plane, based on the sound signals received by three microphones, and can estimate sound signals to be received in an arbitrary position in a space, based on the sound signals received by four microphones.
Moreover, utilizing the results of the processing for estimating sound signals in a plurality of positions with a small number of microphones by the above signal processing technique, the microphone array system of the present invention can perform processing for enhancing a desired sound by synchronous addition of these signals, processing for suppressing noise by synchronous subtraction, processing for detecting the position of a sound source by processing for calculating a cross-correlation coefficient and coefficient comparison processing.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.